Transcript The 4 Stages of Digestion

The Digestive System
Part II
Structures, Functions & Enzymes
The Digestive System
The digestive system is responsible for
the breakdown of large, complex
organic materials into smaller
components that are used by the
tissues of the body
The 4 Stages of Digestion
The 4 stages of digestion
1. Ingestion – taking nutrients into the body
2. Digestion – the breakdown of complex
compounds into smaller components by
enzymes
3. Absorption – the transport of digested
nutrients to the tissues of the body
4. Egestion – the removal of food wastes
from the body
The Mouth
• Digestion begins in the
mouth.
• Teeth helps by
mechanically breaking
down food into smaller
pieces.
• Salivary glands produce
saliva which contains
salivary amylase – an
enzyme that breaks
starch down into simpler
sugars.
The Epiglottis
• To swallow food, the
soft palate raises up to
block off the
passageway to the
nasal passageway and
• The epiglottis flips
down to block the
entrance to the
trachea.
The Esophagus
• Once food leaves the
mouth it is called a
bolus.
• It travels from the mouth
to the stomach along the
food tube known as the
esophagus.
• Peristalsis are wave-like
contractions that push
the bolus along the
entire digestive tract.
The Stomach
• The stomach is the site
of food storage and first
protein digestion
• The rugae (ridges) in
the stomach allow it to
expand from about 50
ml to 1.5 L.
• The stomach has
numerous areas: the
cardiac area, the
fundus, the body and
the pyloric area.
The Stomach
• The cells in the lining of
the stomach secrete
gastric juices.
• Gastric fluids include:
1.
2.
3.
Mucus
Hydrochloric acid
Pepsinogen
The Stomach
• Mucus – protects the
lining of the stomach from
the gastric juices;
• Hydrochloric acid – kills
harmful bacteria and other
harmful substances in
food. It also converts
pepsinogen into its active
form – pepsin, a protein
digesting enzyme.
• Pepsinogen – converts to
pepsin to digest protein.
The Stomach
• Pepsin - breaks down
long amino acid chains in
proteins into shorter
chains called
polypeptides.
Activation
• Pepsiogen +
• HCl
• Pepsin
Active
Enzyme
Protein
Breakdown
• Protein
Breakdown into
• Polypeptides
Sphincters
• Constrictor muscles
the occur along the
digestive tract.
• Sphincters control the
movement of the food
and waste from one
area of the digestive
system to the next.
The Small Intestine & Pancreas
• Most digestion and
nutrient absorption
takes place in the
small intestine.
• It can be divided into 3
zones:
1. Duodenum
2. Jejunum
3. ileum
The Small Intestine & Pancreas
• The chyme that enters the
duodenum from the
stomach is very acidic. It
must be neutralized.
• When acids enter the
small intestine, a chemical
called prosecretin is
converted into the
hormone secretin.
• Secretin travels through
the bloodstream to the
pancreas causing it to
release bicarbonate ions.
The Small Intestine & Pancreas
• Now that the chyme is
alkaline, the pepsin
becomes inactive.
• The pancreas also secretes
other enzymes such as
trypsinogen. Once it
reaches the duodenum the
enzyme enterokinase
converts the inactive
trypsinogen into the active
form – trypsin. Trypsin
further breaks down proteins
into shorter chain peptides..
The Small Intestine & Pancreas
• The pancreas also secretes:
1. erepsins which complete the
digestion of proteins from
short-chain peptides into
individual amino acids.
2. Pancreatic amylase –
further the digestion of
carbohydrates into
disaccharides. These are
finally broken into
monosaccharides by the
enzyme disaccharidases.
The Small Intestine & Pancreas
• The pancreas also secretes:
3. Lipases from the pancreas
break down lipids.
•
Pancreatic lipase breaks
fats into fatty acids and
glycerol.
•
Phospholipase breaks down
phosphlipids.
The Liver and Gall Bladder
• The liver produces bile salts
that speed up the digestion
of fats.
• When fats enter the
duodenum, a hormone
cholecystokinin (CCK) is
released and carried to the
gall bladder. This triggers
the gall bladder to relase the
bile.
• Bile emulsify and breaks
down large fat globules.
The Large Intestine
• Reabsorbs water
• Absorbs some vitamins
• Contains the bacteria, E.Coli
that uses waste materials to
make vitamins B and K.
• Fibre helps to hold some
water in the waste and adds
“bulk” making it easier to
remove from the body.